[CentOS] Re: DNS Server

Mon Jun 26 11:47:36 UTC 2006
Johnny Hughes <mailing-lists at hughesjr.com>

On Mon, 2006-06-26 at 07:38 -0400, Thomas E Dukes wrote:
>  
> > -----Original Message-----
> > From: centos-bounces at centos.org 
> > [mailto:centos-bounces at centos.org] On Behalf Of Johnny Hughes
> > Sent: Monday, June 26, 2006 7:19 AM
> > To: CentOS ML
> > Subject: RE: [CentOS] Re: DNS Server
> > 
> > On Sun, 2006-06-25 at 20:32 -0400, Thomas E Dukes wrote:
> > <snip>
> > 
> > > 
> > > So even if a service such as zoneedit, say they can do 
> > reverse DNS, it 
> > > won't work?
> > > 
> > > I really don't understand how it can work in one direction 
> > and not the 
> > > reverse.  If they can keep up with my IP address and match it to my 
> > > domainanme, seems they could do the reverse.
> > > 
> > 
> > OK ... rather than you staying confused on this issue, I will 
> > try to explain it in basic terms.
> > 
> > DNS converts names to IPs (forward lookups) and IPs to names 
> > (reverse lookups).  
> > 
> > A forward lookup is when you have a name (www.abcxyz.com) and 
> > need a number.  This this case, there is a domain owner and 
> > that domain has it's own DNS Zone.  The owner of that Zone 
> > can put whatever IP addresses
> > (numbers) with names that they want in that zone.
> > 
> > In the case of a forward lookup, there is no predefined zone 
> > at all ...
> > you can have as many names as you want, and since people pay 
> > for it (the name), it stands to reason that will keep it 
> > updated properly.
> > 
> > A reverse lookup is different.  The standard for reverse 
> > lookups break them down in "Class C" blocks (that is, the 
> > first 3 groups of numbers are the network number, the last 
> > group is the host number).  If you have an ip address of:
> > 
> > 192.87.99.234
> > 
> > The network number is 192.87.99.0, the subnet mask is 
> > 255.255.255.0, the host number is 234, and the reverse lookup 
> > domain is:
> > 
> > 99.87.192.in-addr.arpa
> > 
> > All 254 host addresses in that zone are normally assigned 
> > from the owner of that zone from one machine.  If someone 
> > buys the whole class C network, they get to control the zone, 
> > otherwise it is normally controlled by the ISP that owns all the IPs.
> > 
> > It is possible, but not usually done, to break up the reverse 
> > into smaller ranges.
> > 
> > Tom Diehl has already mentioned RFC 2317:
> > 
> > http://www.faqs.org/rfcs/rfc2317.html
> > 
> > Using the techniques there, an ISP _CAN_ transfer control of 
> > some reverse lookup domains.  They will normally not do it 
> > unless you have a fairly large network, however.
> > 
> > I hope this helps you understand that forward zones are 
> > designed to easily break them down into 1 or 2 names ... but 
> > reverse zones are predefined and not designed for less than 1 
> > class C network blocks.
> 
> Hello Johnny,
> 
> I guess that makes sense.  It seems it would create too much work for the
> ISP to handle the reverse lookup for a single IP.  If they dole them out
> that way, they should either do it or delegate them.
> 
> All this is to operate a mail server without bounces.  Is this why it
> recommedned to use your ISP's mail server as smarthost?  Does this mean I
> would be using the ISP's mail server for outgoing mail?  Or is it just
> 'stamped' with the ISP's name to prevent bounces?
> 
> Thanks,
> 
> Eddie

Most ISPs block outbound port 25 traffic now ... only allowing mail
server operation (or even normal sending of e-mail via a client) to be
done out of their mail servers.

I had, for many years, run a mail server on my linux box at home.
Spammers (and viruses) have ruined that option for us. I now have a
domain that I use for e-mail at a hosting provider, as too many servers
now block dynamic ranges and cable/dsl ranges to combat spam.

I have since just setup an NX desktop and use that to get to my mail at
my home desktop when I am not there ... which seems to work OK.

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